The invention relates to a method of recording real-time information and playback parameters related thereto on an information carrier, in which method the real-time information is compressed to units comprising a variable amount of compressed data, and the playback parameters are determined in dependence of the compressed data.
The invention further relates to a recording device for recording real-time information on an information carrier, the device comprising processing means for compressing the real-time information to units comprising a variable amount of compressed data, processing means for generating playback parameters in dependence of the compressed data, and recording means for recording the compressed data and the playback parameters.
The invention further relates to an information carrier carrying real-time information and playback parameters related thereto, the real-time information being represented by units comprising a variable amount of compressed data.
The invention further relates to a playback device for playing back real-time information from the information carrier, the device comprising reading means for retrieving from the information carrier the units and playback parameters, and processing means for processing the playback parameters.
A method of recording real-time information on an information carrier is known from PCT application WO 98/16014 (PHN 16452). Real-time information is information having a real-time nature to be reproduced at a prescribed rate, usually audio or video information, or a combination of audio and video. In the known method audio information is encoded digitally and compressed into units, which represent short segments of the audio signal and usually have a fixed duration of playback time, e.g. 15 msec. The compression rate is variable and responds to the complexity of the real-time information, so it results in a compressed data signal with a variable bitrate. Therefore the length of the units, i.e. the amount of compressed data to be stored per unit, is variable. The reproduction of the audio information requires all compressed data of the respective units, and so reading has to start at the beginning of a unit. The compressed data may be recorded on an information carrier, e.g. an optical disc like the CD, which usually comprises several musical items (usually called tracks), for example each comprising a song. Playback parameters for accessing and reproducing the real-time information are generated for enabling playback functions. For example for an audio CD a Table of Contents (TOC) is generated and stored on the information carrier, which TOC comprises pointers to the locations of the items for accessing the items. Also parameters indicative of the playing time of the items are included in the TOC. Hence the TOC on a CD can be used to access the recorded audio at the start of an item, i.e. at the playing time corresponding to the start of the item. However the TOC cannot be used for directly accessing the recorded audio at a selected point of playing time within an item.
It is an object of the invention to provide recording and payback means for more flexible accessing the recorded real-time information.
For this purpose, the method as described in the opening paragraph is characterized in that the playback parameters comprise an access list having entries, each subsequent entry being assigned to a subsequent interval of a fixed playback time and comprising a pointer to a unit within said interval. This has the effect, that for an arbitrarily selected playing time the pointer of a unit at the selected point of playing time can be easily determined from the access list, in particular because the interval has a fixed size, e.g. 1 second.
The invention is also based on the following recognition. For audio recordings in the prior art, such as on a CD, the TOC contains item start addresses and playing time data, and allows accessing the audio on a item by item basis. Intermediate points in playing time within an item may be calculated from the starting address of the item and the playing time within the item up to the selected point, because there is a fixed relation between the playing time and the amount of data of the stored digital audio signal. For a variably compressed real-time signal no fixed relation exists. Using linear interpolation for an item based on the start and end points of the item from a TOC could result in a large inaccuracy. For example when a musical item starts with a part which is easy to compress, and ends with a part which is difficult to compress part, any interpolation to a point in time in the middle of said item would be severely biased towards the end of the item. Also scanning the music at a higher speed by jumping fixed distances and then reproducing a unit would result in a relatively high speed in the first part, and a low speed in the second part. The inventors have recognized, that the new access list according to the invention allows accurate accessing of selected points of playing time within a recorded real-time signal of a variable bitrate.
An embodiment of the method according to the invention is characterized in that the playback parameters include a length parameter indicative of said fixed playback time. Hence the step size within the access list is set by the interval length. This has the advantage, that the number of entries in the access list can be adapted to the requirements of the recorded signal or the required accuracy.
A further embodiment of the method according to the invention is characterized in that the playback parameters include a margin parameter indicative of a correction of a calculated pointer of a unit within the interval. Access to a point in time within an interval may be required, and interpolation may be used to calculate a pointer. However, as the calculated pointer may be after the actual position of the wanted point in time, a margin may be added for starting the reading process before said ,calculated pointer. By determining the actually required margin during recording, and including the maximum value of said actually required margin in the playback parameters, the playback device can interpolate and correct the interpolated pointer by the margin retrieved from the playback parameters. This has the advantage, that the read process will always start shortly before or at the unit of the selected point in time.
According to the invention the recording device as described in the opening paragraph is characterized as claimed in claim 4. The effects and advantages of the information carrier and the recording and/or playback device have been explained above with reference to the method. Further preferred embodiments of the method, devices and information carrier according to the invention are given in the dependent claims.